Currently rolled metallized film capacitors are usually manufactured by vacuum metallizing one surface of a dielectric film through a mask to provide non-metallized stripes. The metallized film is slit along the non-metallized stripes to provide pairs of film strips having non-metallized, longitudinally extending, opposed margins. A pair of film strips with opposed non-metallized margins are wound in an offset or misregistered relation on an arbor so that the metallized edges of the film strips extend beyond the non-metallized edges. The winding of the film strips is such that the metallized surface of each convolution of one film strip bears against the non-metallized surfaces of the other film strip. Solder is sprayed onto opposed ends to provide porous solder terminations for the subsequent attachment of electrical terminals. Prior to the attachment of the terminals, wax is vacuum impregnated into the wound convolutions to provide a moisture seal to preclude oxidation of the metal on the film strips. The wax may also fill the core hole left by the arbor which is withdrawn following the winding operation. Near the completion of the winding operation a strip of non-coated dielectric material is inserted and wound between the peripheral windings of the metallized film strips so as to prevent short circuiting of the metallized film strips when the outer convolutions including the strip of non-coated dielectric material are heat sealed to prevent unraveling of the rolled film strips.
During the winding operation the film strips are offset from each other to increase the metallized surface areas at the opposed margins which are available to receive the solder terminations. Further, the amount of offset must be sufficient to compensate for variations in the lines of demarcation between the metallized plate areas and the non-metallized margin areas. Inasmuch as the lines of demarcation are set by vapor depositing metal through a mask, there are considerable variations in the linearity of the demarcation lines. As a result, compensating offsets for the variations in the lines of demarcation must be made and there will be a concomitant decrease in the available overlapped metallized areas which determine the capacitance value of the capacitor. The net result of compensating offset is to require the use of wider film strips and thus produce a capacitor of relatively larger physical size.
In the manufacture and design of circuits and circuit boards for use in the telephone and electrical industries there is a continuing need for capacitors having precise capacitance values, small size, stable frequency response characteristics, long life, and good stability under varying temperature and humidity of operating conditions. In general, rolled metallized film capacitors are capable of meeting these needs, however, as circuit design progresses, increased use is being made of integrated circuitry and other semiconductor technology which in turn contemplates the mounting of vast numbers of circuit components on small substrates or printed circuit boards. As this miniaturization progresses there is a continuing requirement to provide compatible, smaller and smaller reliable passive components such as capacitors. One type of capacitor that has been widely used is the small ceramic capacitor. However, ceramic capacitors have a number of inherent deterrents such as temperature sensitivity, inability to self heal, capacitance derogation over a period of time and the characteristic of shorting upon breakdown. Rolled metallized film capacitors do not possess these objectionable deterrents. However, use of rolled film capacitors has been heretofore limited because of their relatively large size, which obviously presents problems in packaging and assembly into miniature circuits.
Considering now the prior art, there is disclosed in U.S. Pat. No. 3,939,440, issued Feb. 17, 1976, to R. D. Berg et al., and assigned to the Western Electric Company, Incorporated, a method of forming a wound resistor-capacitor network wherein a pair of metallized films having non-coated margin areas are simultaneously wound while laser beams scribe lines in the opposed metallized margin areas to define conductive resistor paths on the surfaces of the wound films. In this patent, the non-coated margin is set by depositing metal through a mask, and thus the film must be offset by an amount needed to compensate for linear variations along the demarcation line between the metal coated and non-coated areas. In U.S. Pat. No. 3,597,579, issued Aug. 3, 1971, to R. M. Lumley, and assigned to the Western Electric Company, Incorporated, there is described a method of laser trimming capacitors to value by laser vaporizing sections of capacitor plates or by laser scribing lines on a metallized surface of a capacitor plate to isolate discrete metallized sections from the main metallized plate areas and hence reduce the effective capacitor plate areas.
Another patent showing the use of a laser in the manufacture of rolled film capacitors is U.S. Pat. No. 3,786,224, issued Jan. 15, 1974, to H. Heywang, et al., which utilizes laser beams to remove opposed metallized margins of completely metallized film by directing a laser beam substantially parallel to the metallized surface. In this patent, the rolled film capacitor blank is simultaneously rotated and moved transversely of its axis while the laser beam is vaporizing metal along one margin of one film. This procedure is again practiced to remove the metal along the opposed margin of the other rolled metallized film.
U.S. Pat. No. 2,683,792, issued July 13, 1954, to W. Dublier, and 2,718,180, issued Aug. 23, 1955, to W. Dublier, show electrode discharge means for forming a plurality of finite capacitor plate areas on a metallized film as the film is being advanced to a winding device.